1. Field of the Invention
The present invention relates-generally to a device for passive identification, and more particularly to a method and apparatus for passive identification which includes a remotely modifiable reflectance pattern which is readable at a distance in fog, smoke, dust, during day and night, and under adverse weather conditions and the like.
2. Description of the Related Art
The generalized problem of identification arises in many applications. In one aspect, for example, it is the separation of authentic articles from counterfeit articles. It also arises in motor vehicle control, and, in the battlefield setting, in the identification of friend vs. foe ("IFF").
In the battlefield environment, it is often very difficult to identify and distinguish allied troops ("friends") from enemies ("foes"). Mistaken identifications of foes as friends as well as friendly fire incidents in which friendly troops are mistakenly identified as enemies can have tragic consequences. Thus, various IFF devices have been proposed which improve identification techniques in the combat environment.
Prior art IFF systems have generally utilized a receiver/transmitter unit which, upon receipt of a coded request, transmits an identifying coded response. These devices operate on the principle that only friends will be able to reply properly to the request and if no proper reply is received, the vehicle or person can be assumed to be hostile.
U.S. Pat. No. 5,001,488 to Joguet, for example, discloses a battlefield IFF method and system including an IFF interrogator and responder. Each friendly vehicle is equipped with an IFF receiver antenna and an infrared laser which transmits a laser pulse in response to receipt of an IFF interrogation signal.
Prior IFF techniques, however, have had the disadvantage of either requiring the person or object to be identified to radiate a unique electromagnetic (EM) field or that some type of visual or thermal infrared (IR) symbol be recognizable by active or passive devices, such as lasers or thermal IR detection systems. Because radiated EM signals as well as visual and thermal IR symbols are easily detected and duplicated by an aggressor, foe, or fraudulent counterfeit, prior art IFF systems could be easily compromised, thereby greatly increasing the probability of fratricide or fraudulent counterfeit. The usefulness of visual and thermal IR symbols is also limited by distance, fog, smoke, dust, adverse weather conditions, adverse lighting conditions and the like.
There is a need, therefore, for a fail-safe IFF method which allows for the detection, identification, and differentiation of persons, objects or things in the field, which is capable of differentiating between friends and foes at long distances and in fog, dust and under adverse weather conditions, and which cannot be compromised, detected, or understood by an enemy.
The above is but one example of a situation where identification generally and passive identification in particular is a requirement. As mentioned, there are other systems where such a requirement exists, or where a capability for reliable passive identification could provide substantial benefits. These include prevention of credit card fraud, border control applications, covert law enforcement activities including the interdiction of illegal and/or contraband activities, and many more.